This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9711835.0 filed in Britain on Jun. 6, 1997; the entire content of which is hereby incorporated by reference.
The present invention relates to a semiconductor optical device, such as a laser, and to a method of fabrication thereof, which allows low-loss coupling to an optical fibre.
Semiconductor optical components, such as semiconductor lasers, are widely used. In use, it is often necessary to couple such components to external optical elements. For example, in the case of a semiconductor laser producing a coherent light output, it may be necessary to couple the device to an optical fibre, along which the light is to be directed.
One problem which arises with such coupling is that there can be high losses (up to 10 dB), arising from the different optical modes which exist in the laser and in the fibre. Typically, the optical fibre has a circularly symmetric mode, with a Full Width Half-Max (FWHM) of the order of 7 xcexcm, while the mode in the laser is usually elliptical, with the ratio of the major axis to the minor axis being about 2:1, and with the FWHM being about 1 xcexcm.
One solution to this problem is to use lenses, but this is expensive, and is not usually practical if it is desired to make an array of lasers. Ideally, it should be possible simply to place the end of the fibre against the output face of the laser, and join them using butt-joint coupling.
If this is to be possible, the mode size at the output of the laser must be increased, so that it is a better match to the mode within the fibre. One such proposal is disclosed in U.S. Pat. No. 5,278,926. In this document, it is proposed that the semiconductor optical component should include two buried heterostructure optical waveguides, namely an active waveguide and a passive waveguide which are superposed over at least a part of their lengths, the transverse cross-sectional area of the active waveguide decreasing over a mode transition region to couple a narrow optical mode, which is guided by the active waveguide, to a wide mode, which is guided by the passive waveguide.
One object of the present invention is to provide a fabrication process which allows relatively easy manufacture of an optical component such as a laser, which may be coupled to an optical fibre.
A further object of the invention is to define a structure which allows easy coupling to an optical fibre.
The present invention relates to a method of fabricating the semiconductor laser which allows the use of standard fabrication techniques, without requiring particularly tight manufacturing tolerances. Moreover, the invention relates to the structure made by this fabrication process. In particular, there is also disclosed a structure with an asymmetrically tapered waveguide.